Field of the Invention
The present invention relates to a tool gravity center position estimation device that estimates a gravity center position of a tool and a machine tool using the estimated tool gravity center position.
Description of the Related Art
Conventionally, there is known a machine tool having a function of changing an operating speed of a tool changer according to a weight of an attached tool. Such a machine tool uses this function to operate the tool changer at an optimum speed, which allows the machine tool to be driven at a sufficient speed while suppressing an impact on the machine or heat generation from a motor.
Further, there is known a machine tool having a function of estimating moment of inertia of a spindle upon attachment of a tool from acceleration of the spindle upon rotation thereof. The function of estimating moment of inertia of a spindle of such a machine tool allows operation of the spindle to be controlled appropriately according to the moment of inertia of the tool.
JP 11-188557 A discloses a changing arm type tool changer capable of shortening tool change time by detecting a drive torque required to rotate a changing arm that holds a tool, estimating a weight of the tool from the detected drive torque, and automatically setting an operating speed of the changing arm based on the estimated tool weight.
JP 05-138502 A discloses a numeric-control machine tool that detects, when a constant power is supplied to a spindle rotating motor, a time required for a spindle rotating speed to reach a certain set value to calculate moment of inertia of a spindle and compares the calculated moment of inertia with a spindle rotating speed command value to determine whether or not the spindle can be rotated as instructed.
JP 2013-186545 A discloses a spindle positioning device that estimates moment of inertia of a spindle from a magnetic flux density command to be issued to a motor and a magnetic flux density estimation value, and a motor speed, and changes an output command value to be issued to the motor according to the estimated moment of inertia.
A device that changes an operating speed of a machine according to a tool weight, like the tool changer disclosed in JP 11-188557 A, can be driven while suppressing an impact on the machine or heat generation from a motor; however, sometimes the impact on the machine or a load on the motor cannot be estimated accurately only with information of the tool weight.
Further, the devices disclosed in respective JP 05-138502 A and JP 2013-186545 A can control the operating speed of a motor for the spindle by calculating the moment of inertia of the spindle; however, also in this configuration, sometimes the impact on the machine or a load on the motor cannot be estimated accurately only with information of the moment of inertia of the spindle.
In order to estimate the impact on the machine or load on the motor more accurately, it is preferable to use not only the tool weight or moment of inertia, but also information of a gravity center position of the tool. However, it is troublesome for a user to measure or calculate the gravity center position of each tool in advance, which may make it difficult to use the gravity center position information of the tool so as to perform appropriate operation setting of the machine tool.